Method of removing acetylenes from diolefin mixtures



Aug. 28, 1951 c. E. MORRELL. ETAL METHOD OF REMOVING ACETYLENES FROM DIOLEFIN MIXTURES N LUS .HNHK

Filed Aug. 4, 1942 Unox Tuluvl WOR' (Nlun.

Patented Aug. 28, 1951 `METHOD OF REMOVING ACETYLENES FROM DIGLEFIN MIXTURES Charles E. Morrell, Roselle, and Miller W. Swaney, Linden, N. J., assignors to Standard Oil Development Company, a corporation of Delaware Application August 4, 1942, Serial No. 453.544

y 9 Claims. l

This invention relates to improvements in the process for separating dlolens from hydrocarbon mixtures containing diolens and acetylenes and relates particularly to the separation of alkyl acetylenes in the process for the separation ano segregation of high purity diolens from the same hydrocarbon mixture.

The chief source of diolelns is in hydrocarbon mixtures obtained by cracking petroleum oils. The cracked mixture is first fractionated by distilling the cracked hydrocarbons to obtain a cut containing only hydrocarbons having the same number of carbon atoms to the molecule, for example 4, or 6. A11 such fractions for example having 4 carbon atoms to the molecule contain both the desirable diolen butadiene and small traces of alkyl acetylenes in concentrations ranging up to several thousand parts per million. For example, 4 carbon atom mixtures of hydrocarbons obtained by pyrolyzing petroleum oils, by analysis, were found to contain from 500 to 800 parts per million of mixed ethyland vinyl-acetylene. This process will be described with reference to C4 hydrocarbons but may also be used for C5 or Ce hydrocarbons.

In the extraction of butadiene from a hydrocarbon mixture composed of hydrocarbons having 4 carbon atoms to the molecule and also containing acetylenes and diolens, the alkyl acetylenes are usually concentrated along with the butadiene. Consequently the high purity butadiene produced may be contaminated with fairly large amounts of these acetylenes which are undesirable for the purposes for which the butadiene has been segregated.

An object of this invention is to provide means for the separation or rddance of the acetylenes that generally separate with the butadiene on the extraction of the butadiene from the hydrocarbon mixture.

According to this invention it has been found that both ethyl acetylene and vinyl acetylene possess strong tendencies to polymerize to higher molecular weight substances in contact with heated basic cuprous salt solutions such as ammoniacal cuprous acetate and `pyridine cuprous sulfate solutions. For example, when pure ethyl acetylene is heated with an ammoniacal cuprous acetate solution in which it is quite soluble, it is quickly converted to higher boiling oily polymers. Under similar circumstances it was found that vinyl acetylene was converted to a solid insoluble powdery polymer. Both of these polymers are non-explosive and therefore are easily removed from C; mixtures thus treated.

(Cl. 26o-6815) When a cracked C4 cut containing 25% butadiene. 800 parts per million of mixed alkyl acetylenes, and the remainder essentially butenes, is extracted (batch or continuously) at a temperature of about 0 C. with an ammonacal cuprous acetate solution containing about 3 moles per liter of copper, 4 to 5 moles of acetate and 10 to ll moles of total ammonia, the butadiene is removed practically quantitatively from this C4. mixture, leaving essentially butenes. In addition, the acetylenes are also removed quantitatively from the C4 hydrocarbon mixture ane, enter the copper solution as soluble copper acetylides. Now, if this solution is immediately heated to about '70 C. the desorbed butadiene gas which is ashed off will carry a large part of the total acetylenes with it and this may reach a concentration of several thousand parts per million (on butadiene basis). On the other hand, when this solution is heated at this higher temperature without being desorbed (e. g., under pressure) the acetylenes are found to be readily transformed into harmless higher molecular weight polymers.

This principle is used in freeing butadiene and other hydrocarbons of alkyl acetylenes.

Specically in the extraction of butadiene from cracked C4 cuts using basic cuprous salt solutions as selective solvents, the extraction or concentration operation is performed in such a manner that the cold copper salt solution is passed countercurrently to the C4 hydrocarbon so as to remove substantially all of the butadiene, accompanied by complete transfer of alkyl acetylenes from the C4 phase to the copper' solvent. This rich solvent (containing butadiene and acetylenes) is then heated and desorbed countercurrently (at about '70 C.) in a packed or other type of tower while maintaining a considerable amount of reux on the desorption tower. This reflux consists of maintaining the downowing copper solution at a low temperature in the top of the desorber and supplying heat to the lower regions of the desorber tower. The purpose served by reflux desorption is as follows:

When a rich copper solution containing both absorbed butadiene and acetylenes is heated and desorbed, for example by flashing, the butadiene escapes carrying with it considerable quantities of acetylenes, although some of the latter are polymerized by the hot copper solution to high molecular Weight substances. However, when a cold rich solution is fed into the top of a countercurrently operated desorber tower to which heat accedas is supplied by means of a '70 C. bottom reboiler, any acetylenes which are not polymerized immediately in the lower hot regions are desorbed and carried upward in fairly high concentrations with the desorbed butadiene which must then pass through the cold solution (reflux") in the top of the desorber. In this way the acetylenes are reabsorbed and again carried back down to the heated regions of the desorber tower where they are largely polymerized. Those acetylenes which do not polymerize or stay in the hot copper solution are again carried up to the tower with the desorbed butadiene. only to be reabsorbed by the cold reflux and eventually completely polymerized by the hot solution. In this way it is possible to produce high purity butadiene substantially free of alkyl acetylenes (ethyl and vinyl), practically irrespective of the concentration of acetylenes in the butadienecontaining C4 cut extracted.

By this means of dissipating or destroying acetylenes by hot copper solutions, butadienecontaining cracked C4 cuts of practically any acetylene content can be continuously extracted without encountering precipitation of explosive copper acetylides.

A further application of the dissipation of acetylenes by polymerization by hot copper solutions consists of taking the hot lean solution leaving the desorber tower and sending it to a soaking drum where it can be kept hot for practically any desired length of time in order to effect additional polymerization of acetylenes before this lean solution is cooled and returned (recycled) to the absorber for further extraction Of cracked C4 feed.

A cracked C4 cut of the following approximate composition has been extracted continuously with an ammoniacal cuprous acetate solution of the following approximate composition:

Cracked C4 Out Copper Solvent 25 mol per cent butadlene-... 3 moles per liter of cuprous. 17 mol per cent butenes-2. 0.1 mole per liter of cupric. 35 mol per cent butene-l. 4 moles per liter of acetate. 20 mol per cent isobutene... l1 moles per liter oi total ammonia. BOO-1000 P. P. M. alkyl acetylenes. Traces of Cr and By proper control of desorber cold reflux butadiene products of 99.5+% purity were produced containing as little as 300-400 parts per million or less of acetylenes, or less than ten per cent of the acetylenes entering the copper solvent,

at least 90% or more being polymerized to high molecular weight polymers during the extraction step. This great reduction in acetylenes was accomplished by sending less than 20% of the cold solution to the top of the desorber as reflux, the remainder being preheated to desorption temperature and injected into the middle cf the desorber tower. Obviously by employing higher reilux," the acetylene concentration in the butadiene product can be reduced substantially to zero.

Example 1 To a 0 cc. quantity of an ammonical cuprous acetate solution containing 3 moles per liter of cuprous complex was added several grams of pure vinyl-acetylene. The mixture was heated (enclosed) at 70 C. for a short time, during 4 which all the vinyl-acetylene was converted to a solid powdery material insoluble in all solvents and common acids, being dlssoved only by hot sulfuric-chromic acid mixture. This solid polymer is easily filterable from the solution.

Example 2 When pure ethyl-acetylene was heated as in Example 1, it was likewise quantitatively polymerized. but to a heavy oily liquid with an ethereal odor, soluble in most solvents.

Eample 3 During a period of several weeks a mixture of C4 hydrocarbons obtained by cracking of petroleum oils and containing 800-1000 parts per million of alkyl acetylenes was extracted continuously with a batch of ammoniacal cuprous acetate solution (containing 3 moles per liter of cuprous complex) which was circulated through several thousand complete cycles in an extraction apparatus consisting of a cold absorber tower and a heated desorber tower, and cold solution reflux was maintained on top of this countercurrent desorber tower. The high-purity butadiene produced contained only about 10 per cent of the alkyl acetylenes entering the copper solution fromv the C4 cut extracted, and the quantity of acetylenes remaining in the copper solution after desorption was negligible. The remainder (approximately were polymerized to the harmless polymers described in Examples 1 and 2.

coincidental with the selective polymerization of alkyl acetylenes in hot copper solutions over butadiene, one can also advantageously eiect the polymerization of allenes, R-CH=C=CH2, selectively over butadiene. Cracked C4 cuts usually contain, in addition to traces of alkyl acetylenes, allenes as well, for example, propadiene, this material boiling higher (-34 C.) than the usual C3 distillation range and therefore being difficult to separate from the C4 out by distillation. Although propadiene occurs in .cracked C4 cuts in only low concentrations, it is a diolefin and is therefore concentrated by copper salt extraction along with butadiene. In order, therefore, to prevent this aliene from appearing in appreciable concentrations in the desorbed butadiene product, We have found that it polymerizes quite readily in copper solutions when heated, thus:

Example 4 Into a glass tube were placed 10 cc. of ammoniacal cuprous acetate solution (containing 3 moles per liter of cuprous complex) and several grams of pure propadiene. After sealing this tube it was heated to '70 C. for several hours and re-opened after cooling to room temperature. Thus the propadiene was found to have polymerizedzqxuantitatively to a heavy clear liquid polymer-with a musty odor, this polymer forming a separate layer on top of the copper solution.

Referring to the drawing where the iiow of materials is shown diagrammatically, numeral I denotes a pipe through which a hydrocarbon C4 mixture containing acetylenes and butadiene is passed to pipe 2 and into a turbine-type mixer 3 together with ammoniacal cuprous acetate solution which is introduced through pipe 4 into pipe 2. After being thoroughly mixed the mixture is passed through pipe 5 into separator 6 where the unabsorbed hydrocarbon gases are 1emoved through pipe l and passed to turbine-type mixer 8 together with an ammoniacal cuprous acetate solution which is introduced into pipe 1 through pipe 9, being obtained from settler I0. The mixture of ammoniacal cuprous acetate solution and hydrocarbon gases is passed through pipe II into settler I2 where the cuprous acetate ammoniacal solution is removed through pipe 4 and the unreacted hydrocarbon gases are removed through pipe I3 and passed through pipe I4 into turbine-type mixer I5 together with a new charge of ammoniacal couprous acetate solution substantially free of any oleflns or dioleflns obtained through pipe I6. The mixture is then passed through pipe I1 into settler In where the unreacted gases are removed through pipe I8. The cuprous acetate ammoniacai solution removed from settler E is passed through pipe I9 into separator 20, being heated to a temperature ranging from 10 to 30C. The absorption temperature used generally ranged from about 10 C. to 25 C. with pressures of about 19 to about lbs. per square inch gauge. The pressure used in this separator 20 is generally about 80 lbs. per square inch gauge. The gases that are freed in this settler 20 are rem'oved through pipe 2| and passed through pipe 2 into turbine mixer 3. The ammoniacal cuprous acetate solution with the diolen in solution is removed by means of pipe 22 and p-assed to the upper part of desorber 23, where it rlows downwardly in countercurrent flow to butadiene and some acetylenes to the bottom part of the tower where a temperature voi? about 10 C. to 85 C. is maintained at a pressure of about 10 lbs. per square inch gauge. In this tower a major portion of acetylenes are polymerized to harmless polymers. The hot ammoniacal cuprous acetate solution with the last traces of acetylides in solution is passed through pipe 24 to soaking drum 25 where the acetylides are more completely polymerized. The cuprous acetate solution is recycled through pipe 26 to the bottom part of the desorber 23. Side streams are removed from this desorber by means of pipes 21 and 28. Those removed through pipe 21 are passed through heater 29 and returned to the bottom part of the tower through pipe 30 while the ammoniacal cuprous acetate solution removed through pipe 28 is recycled through cooler 3I and passed to the upper part of the tower by means of pipe 32.

of the desorber 23. From the desorber through pipe 33 is passed substantially pure butadiene to wash tower 34 where it is washed with water supplied by means of pipe 35 to remove any ammonia or other water soluble constituents, the water being removed through pipe 3B and the butadiene being removed through pipe 31. From the soaking drum through pipe 38 is passed an ammoniacal cuprous acetate solution to the second desorber 39 where is it subjected to further heat of about 80 C. to distill over allenes if any are present, this being removed through pipe 40 and passed through to wash tower 4I where it is washed with water supplied by pipe 42 and substantially pure allene is obtained through pipe 43, the water being removed by pipe 44. From the second desorber 39 is removed substantially pure ammoniacal cuprous acetate solution which may be supplied with further cuprous acetate and ammonia by means of pipe 45 and is then cooled and recycled for use in the absorption of butadiene, acetylenes and allenes.

We claim:

1. An improved copper ammonium acetate absorption and purification method for separating butadiene from a hydrocarbon mixture containing it together with butenes and small amounts of acetylenes, comprising thc steps of contacting said mixture with a solution of copper ammonium acetate to obtain a rich solution containing butadiene and acetylenes, subsequently desorbing the butadiene from said rich solution at a`temperature of about '10 C. to 85 C. at a pressure of about 10 pounds per square inch gauge, whereby .a lean solution substantially free of butadiene is obtained and exposing said lean solution to conditions causing polymerization of acetylenes.

2. In the method described in claim l, removing a resulting solid lterable polymer of vinyl acetylene present in said acetylenes from the exposed lean solution.

3. In the method dened by claim 1. causing polymerization of vinyl acetylene present :in said acetylenes to a solid lterable polymer in the exposed lean solution.

4. An improved copper ammonium acetate absorption and puriiication method for separating butadiene from a hydrocarbon mixture containing butadiene together with small amounts of ethyl acetylene and vinyl acetylene. comprising the steps of contacting said mixture with a solution of copper ammonium acetate to obtain rich solution containing butadiene and said acetylenes, subsequently heating said rich solution at temperatures in the range from about 25 C. to a temperature of about '70 C. to desorb butadiene therefrom, and further heating the resulting lean solution containing the acetylenes to temperatures of about C. to 85 C. so as to polymerize the vinyl acetylene to a solid polymer easily ilterable from the solution and to polymerize the ethyl acetylene to a heavy liquid oily polymer.

5. A process of concentrating butadiene, which comprises heating a basic cuprous salt solution containing absorbed butadiene and acetylenes at temperatures of about 70 to 85 C., desorbng the butadiene from said solution, and selectively polymerizing the acetylenes in said solution thus being heated.

6. A process of concentrating a conjugated diolen of high purity which comprises contacting a hydrocarbon mixture containing the diolerln. olens, and acetylenes, with a basic solution of cuprous salt, separating unabsorbed hydrocarbons from the basic solution containing the diolens and acetylenes absorbed therein, heating said basic solution containing the absorbed diolen and acetylenes to elevated temperatures in the range of about 70 C. to about 85 C. to desorb the diolens, contacting the resulting desorbed gaseous dioleiin with a'part of the basic cuprous salt solution at substantially lower temperatures to reabsorb and selectively polymerize the acetylenes in the basic cuprous salt solution as it is heated to elevated temperatures in the range of about 70 C. to 85 C.

'7. A process of concentrating a diolefin having 4 to 6 carbon atoms to the molecule which comprises heating a basic cuprous salt solution having the diolefin and acetylenes absorbed therein from a temperature of about 25 C. to an elevated temperature in the range of 70 C. to 85* C. as the solution is passed from an upper part to a lower part of a. desorption zone to regenerate the diolefin and polymerize the acetylenes, passing the regenerated diolen countercurrently in contact with downowing basic cuprous salt soiution having a lower temperature at an upper part of the desorption zone to reabsorb acetyienes released with the Aregenerated diolen.

8. The process dened in claim 6, in which the diolen is butadiene and the basic cuprous salt solution is an ammoniacal cuprous acetate solution, and wherein the solution containing the absorbed butadiene with acetylenes is heated from below 30 C. to above 60 C. in said desorption zone.

9. The process dened in claim 6, in which a portion of the solution from which the diolefln has been desorbed is withdrawn from the desorption zone. cooled to about 25 C.. and recycled as a reux to the upper part of desorption zone.

CHARLES E. MORRELL. MILLER w. SWANEY.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Num` er Name Date 2,336,643 Schulze Dec. 14, 1943 2,399,882 Morrell et ai May 7, 1946 2,463,846 Bain et a1.- Mar. 8. 1949 v FOREIGN PATENTS Number Country Date 976 Great Britain Jan. 13, 1913 OTHER REFERENCES Lure et a1., Sintetioheskii Kauchuk 6, 19-29 (1934 

1. AN IMPROVED COPPER AMMONIUM ACETATEE ABSORPTION AND PURIFICATION METHOD FOR SEPARATING BUTADIENE FROM A HYDROCARBON MIXTURE CONTAINING IT TOGETHER WITH BUTENES AND SMALL AMOUNTS OF ACETYLENES, COMPRISING THE STEPS OF CONTACTING SAID MIXTURE WITH A SOLUTION OF COPPER AMMONIUM ACETATE TO OBTAIN A RICH SOLUTION CONTAINING BUTADIENE AND ACETYLENES, SUBSEQUENTLY DESORBING THE BUTADIENE FROM SAID RICH SOLUTION AT A TEMPERATURE OF ABOUT 70* C. TO 85* AT A PRESSURE OF ABOUT 10 POUNDS PER SQUARE INCH GUAGE, WHEREBY A LEAN SOLUTION SUBSTANTIALLY FREE OF BUTADIENE IS OBTAINED AND EXPOSING SAID LEAN SOLUTION TO CONDITIONS CAUSING POLYMERIZATION OF ACETYLENES. 